Nano-gap grating devices with enhanced optical properties and methods of fabrication

ABSTRACT

A method of producing a grating structure comprises the steps of forming a stamp from flexible plastic material, the stamp including a negative of a periodic grating pattern on a first surface; forming an ink by applying a polymer film to the stamp, the ink including a first surface and an opposing second surface, wherein the first surface of the ink contacts the first surface of the stamp such that the ink retains a positive of the periodic grating pattern; placing the ink and the stamp on a substrate such that the second surface of the ink contacts an upper surface of the substrate; and removing the stamp from the ink by applying a tensional force to one edge of the stamp.

RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 14/081,353, filed on Nov. 15, 2013 and entitled“NANO-GAP GRATING DEVICES WITH ENHANCED OPTICAL PROPERTY ANDFABRICATIONS THEREOF,” and which issued as U.S. Pat. No. 10,073,200 onSep. 11, 2018 (“the '200 patent”) and claims priority benefit withregard to all common subject matter. The '200 patent claimed prioritybenefit of U.S. Provisional Application No. 61/850,232, filed Feb. 11,2013, and entitled “NANO-GAP GRATING DEVICES WITH ENHANCED OPTICALPROPERTY AND FABRICATIONS THEREOF.” The identified earlier-filedprovisional application is hereby incorporated by reference in itsentirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant No.ECCS-1102070 awarded by the National Science Foundation and Grant No.W15QKN-11-9-0001-RPP1-H awarded by the Nano Technology EnterpriseConsortium (NTEC). The Government has certain rights in the invention.

BACKGROUND 1. Field

Embodiments of the invention relate to structures for improving opticalimaging and methods of their fabrication.

2. Related Art

Microscopic imaging is utilized for studying small objects in fieldssuch as medical development, biological research, cancer research,metallurgy, and others. Imaging of microscopic objects often encountersthe diffraction limit when trying to image increasingly small objects.Fluorescence spectroscopy can be utilized in ultrasensitive chemical andbiological threat sensors. But fluorescence spectroscopy suffers fromlow image contrast and a limit on the detection capabilities. Uniform,periodic grating structures have been developed to offer improvement inmicroscopic imaging and fluorescence spectroscopy. However, theimprovements may be limited and the production of the grating structuresmay require the usage of costly fabrication equipment and complexmanufacturing techniques, leading to a high cost of the gratingstructures.

SUMMARY

Embodiments of the invention solve the above-mentioned problems andprovide a distinct advance in the art of microscopic imaging andfluorescence spectroscopy. More particularly, embodiments of theinvention provide grating structures with enhanced optical propertiesand methods of their fabrication.

A first embodiment of the invention provides a grating structurecomprising a substrate, a base layer, and a first functional layer. Thebase layer is positioned on the substrate and includes a first surfacewith a plurality of grating elements positioned adjacent one another andan opposing second surface in contact with a surface of the substrate.The grating elements include a longitudinal peak and a longitudinalvalley. The functional layer is positioned on the second surface of thebase layer and provides electromagnetic field enhancement in thevicinity of the grating structure.

A second embodiment of the invention provides a method of producing agrating structure. The method comprises the steps of forming a stampfrom flexible plastic material, the stamp including a negative of aperiodic grating pattern on a first surface; forming an ink by applyinga polymer film to the stamp, the ink including a first surface and anopposing second surface, wherein the first surface of the ink contactsthe first surface of the stamp such that the ink retains a positive ofthe periodic grating pattern; placing the ink and the stamp on asubstrate such that the second surface of the ink contacts an uppersurface of the substrate; and removing the stamp from the ink byapplying a tensional force to one edge of the stamp.

A third embodiment of the invention provides a method of producing a.The method comprises the steps of forming a stamp by applying a flexibleplastic material to a mold which includes a periodic grating pattern,wherein the stamp retains a negative of the grating pattern on a firstsurface; forming an ink by applying a polymer film to the stamp, the inkincluding a first surface and an opposing second surface, wherein thefirst surface of the ink contacts the first surface of the stamp suchthat the ink retains a positive of the periodic grating pattern; placingthe ink and the stamp on a substrate such that the second surface of theink contacts an upper surface of the substrate; removing the stamp fromthe ink by applying a tensional force to one edge of the stamp; andapplying a functional layer to the first surface of the ink.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the invention will be apparent from the followingdetailed description of the embodiments and the accompanying drawingfigures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a perspective view of a grating structure including a firstfunctional layer, a base layer, and a substrate, constructed inaccordance with various embodiments of the invention;

FIG. 2 is a perspective view of the base layer and the substrate fromthe grating structure of FIG. 1, the base layer including a plurality ofnanogaps;

FIG. 3 is a perspective view of the grating structure with the firstfunctional layer being deposited at an angle away from normal to theplane of the grating structure;

FIG. 4 is an enlarged view of a portion of the grating structure of FIG.3;

FIG. 5 is a perspective view of the grating structure with the firstfunctional layer being deposited normal to the plane of the gratingstructure and a second functional layer being deposited at an angle awayfrom normal to the plane of the grating structure;

FIG. 6 is an enlarged view of a portion of the grating structure of FIG.5;

FIG. 7 is a flow diagram of at least a portion of the steps of a methodof producing a grating structure;

FIG. 8 is a perspective view of a mold created from a modified opticaldisc;

FIG. 9 is a perspective view of the mold coated with a plastic materialto form a stamp;

FIG. 10 is a sectional view of the mold and the stamp from FIG. 9 cutalong the line 10-10;

FIG. 11 is a perspective view of the mold and the stamp with a portionof the stamp removed to create a small stamp;

FIG. 12 is a perspective view of the stamp placed on a temporarysubstrate;

FIG. 13 is a perspective view of the stamp on the temporary substratecoated with a polymer film to create an ink;

FIG. 14 is a sectional view of the stamp and the ink from FIG. 13 cutalong the line 14-14;

FIG. 15 is a perspective view of the stamp and the ink placed on apermanent substrate;

FIG. 16 is a sectional view of the stamp and the ink from FIG. 15 cutalong the line 16-16;

FIG. 17 is a perspective view of the stamp and the ink on the permanentsubstrate depicting the stamp being removed from the ink;

FIG. 18 is a flow diagram of at least a portion of the steps of a methodof producing a mold that includes a grating structure;

FIG. 19 is a sectional view of a first type of optical disc with a metallayer and a transparent side in which the metal layer is closer to thetransparent side;

FIG. 20 is a sectional view of the first type of optical disc in whichthe metal layer and the transparent side have been removed;

FIG. 21 is a sectional view of a second type of optical disc with ametal layer, a transparent side, and a label side in which the metallayer is not closer to the transparent side; and

FIG. 22 is a sectional view of the second type of optical disc in whichthe metal layer and the label side have been removed.

The drawing figures do not limit the invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying drawings that illustrate specificembodiments in which the invention can be practiced. The embodiments areintended to describe aspects of the invention in sufficient detail toenable those skilled in the art to practice the invention. Otherembodiments can be utilized and changes can be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense. Thescope of the present invention is defined only by the appended claims,along with the full scope of equivalents to which such claims areentitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the technology can include a variety of combinations and/orintegrations of the embodiments described herein.

A grating structure 10 with nanogap features, constructed in accordancewith various embodiments of the invention, is shown in FIGS. 1, 3, and 4and may broadly comprise a substrate 12 and an array 14 of gratingelements 16. Various embodiments of the invention can provide opticalwave guiding and imaging beyond the diffraction limit. The invention maybe utilized in a sensing or imaging system which may improve thedetection limits of harmful biological and chemical agents in food downto pico or femtomolar concentration levels. Similarly the invention maybe used in anti-terrorism to detect any trace quantities of bio orchemically hazardous material. Embodiments of the invention may also beutilized in studying single molecule fluorescence phenomena in realtime, enhancing surface-enhanced Raman spectroscopy (SERS), and thelike.

The substrate 12, as shown in FIGS. 1-3, generally provides a structuralbase or foundational support for the grating elements 16 and may beformed from silicon, glass, or combinations thereof. The substrate 12may include an upper surface 18 that receives the grating elements 16.The upper surface 18 may be planar and smooth so as to easily bond withthe grating elements 16.

The array 14, as shown in FIGS. 1 and 3, is arranged on the substrate 12so that the grating elements 16 are parallel and positioned abutting oneanother. Each grating element 16 is generally elongated, relativelynarrow, and is formed with a longitudinal peak 20 positioned next to alongitudinal valley 22. In some embodiments, the longitudinal axis ofthe grating elements 16 may be straight, while in other embodiments, thelongitudinal axis may be curved. In some embodiments, the peak 20 mayhave a constant and continuous height along the length of the gratingelement 16, while in other embodiments, the peak 20 may have a variableheight along the length of the grating element 16.

An exemplary grating element 16, as seen in FIG. 1, may have across-sectional profile that is a roughly half sine wave with the peak20 having a generally rounded shape and the valley 22 being generallyflat. An exemplary grating element 16 may have a width or pitch ofapproximately 400 nanometers (nm). The width of each grating element 16may vary depending on the application for which the grating structure 10is used. An exemplary peak 20 may have a height relative to the valley22 of approximately 60 nm. In other embodiments, the grating element 16may have a cross-sectional profile that is a roughly sine wave shape, aroughly triangle wave shape, a roughly square wave shape, a roughlysawtooth shape, variations thereof, or combinations thereof.

Each grating element 16 may include a base layer 24 and a firstfunctional layer 26. The base layer 24, as seen without the firstfunctional layer 26 in FIG. 2, may be positioned on the substrate 12 andmay include a lower surface 28 which contacts and adheres to the uppersurface 18 of the substrate 12. The base layer 24 may be formed from apolymer material or a polymer film such as polymethylsilsesquioxane(PMSSQ) and may have the same cross-sectional profile as the gratingelement 16 including the peak 20 and the valley 22. The base layer 24may also be considered an ink.

The base layer 24 may further include a plurality of nanogaps 30, bestseen in FIG. 2, wherein each nanogap 30 is an elongated, generallynarrow gap or opening in the material of the base layer 24. Exemplarynanogaps 30 may have a width ranging from approximately 20 nm toapproximately 30 nm, while the length of the nanogaps 30 may vary moregreatly. In some embodiments, the nanogaps 30 may be randomly orientedand randomly distributed primarily in proximity to the edges of thearray 14. In other embodiments, the nanogaps 30 may be more uniformlydistributed across the array 14. In addition, the nanogaps 30 maygenerally be oriented or aligned with one another. In still otherembodiments, there may be a combination of randomly oriented anddistributed nanogaps 30 and more uniformly oriented and distributednanogaps 30.

The first functional layer 26, as seen in FIGS. 1, 3, and 4, generallyprovides electromagnetic field enhancement in the vicinity of thegrating structure 10. The first functional layer 26 may be applied orformed such that it does not fill in or completely cover the nanogaps 30of the base layer 24. The first functional layer 26 may include either aplasmonic component or a photonic component. In embodiments of the firstfunctional layer 26 with plasmonics, the first functional layer 26primarily includes one or more layers of metal. An optional lower metallayer may provide improved adhesion between the base layer 24 and anupper layer of metal. An exemplary lower metal layer may include a thinlayer of titanium, approximately 2 nm thick. A main upper layer of metalmay provide plasmonic functionality. An exemplary metal for the uppermetal layer is silver, approximately 100 nm thick, deposited on thefirst lower layer of metal. Silver is often utilized as the plasmonicmaterial because it may allow or promote fluorescence in variousapplications of the grating structure 10 to a greater extent than othermetals. In addition, silver may have a lower energy loss than othermetals. Other metals can be used for either the first lower adhesionlayer or the second, upper metal layer including silver, titanium, gold,chromium, alloys, or combinations thereof. In some embodiments, theplasmonic first functional layer 26 may further include a thin layer ofdielectric or insulating material, such as silicon dioxide,rhodamine-doped PMSSQ, or similar materials positioned on the metal. Thelayer of dielectric may have a thickness ranging from approximately 10nm to approximately 30 nm.

In embodiments of the first functional layer 26 with photonics (alsoreferred to as photonic crystals), the first functional layer 26primarily includes one or more layers of dielectrics. An exemplaryphotonic first functional layer may include titanium oxide (TiO₂), witha thickness ranging from approximately 100 nm to approximately 200 nm,deposited on the base layer 24. When the grating structure 10 is usedfor photonic applications, the thickness of the base layer 24 may bevaried as well to provide different performance characteristics.

The first functional layer 26 may further include nanogaps 32 as well,seen in FIGS. 3 and 4, depending on the angle of deposition of theplasmonic or photonic material onto the base layer 24. If the plasmonicor photonic material of the first functional layer 26 is deposited ontothe base layer 24 at an angle that is roughly normal to the plane of thesubstrate 12 and the base layer 24, as shown in FIG. 1, then no nanogaps32 in the first functional layer 26 are formed. If the plasmonic orphotonic material is deposited at an angle, such as θ shown in FIG. 3,away from the normal, then nanogaps 32 may be formed in parallel withthe grating elements 16. The deposition angle may range fromapproximately zero degrees to approximately 85 degrees from planarnormal, with a range from approximately 65 degrees to approximately 80degrees providing optimal results. Typically, the plasmonic or photonicmaterial is also deposited in a direction that is transverse to thelongitudinal axis of the grating elements 16.

When the first functional layer 26 is deposited at an angle other thanplanar normal, each grating element 16 may include three regions, asseen in FIGS. 3 and 4, instead of just the two discussed above. Theregions may include the nanogap 32, a tip 34, and a plateau 36.Furthermore, the tip 34 may include a plurality of nanospurs 58. Whenviewed in cross-sectional profile, the nanogap 32 may present a lowpoint for the grating element 16, while the tip 34 may present a highpoint, with an angled, generally smooth surface therebetween. Theplateau 36 may have a rounded shape that falls from the tip of onegrating element 16 to the nanogap 32 of the adjacent grating element 16.In an exemplary embodiment in which the first functional layer 26 wasdeposited at an angle of approximately 76 degrees away from planarnormal, the nanogap 32 has a width ranging from approximately 10 nm toapproximately 30 nm, the tip 34 has a width ranging from approximately10 nm to approximately 30 nm, and the plateau 36 has a width ofapproximately 90 nm. The nanospurs 58 may include or may form aplurality of peaks abutting one another along the length of the tip 34,as shown in FIGS. 3-6. Each nanospur 58 may have a shape of roughly atriangle, roughly a sawtooth, roughly a half sine wave, variationsthereof, or combinations thereof. At the edges of each nanospur 58, orwhere the nanospurs 58 join with one another, there may be a sharppoint.

The nanogap 32 and the tip 34 may behave like electromagnetic fieldconcentrators, wherein the nanogap 32 acts as a lightning rod and thetip 34 acts as a nano antenna. The plateau 36 experiences interferencefrom the two distinct electromagnetic fields resulting in eitherconstructive or destructive interference. The large electromagneticfields produced in the nanogap 30, the tip 34, and the plateau 36 are aresult of the localized electromagnetic field enhancement. When thegrating structure 10 is utilized in fluorescence imaging, either thelightning rod, the nano antenna, or the constructive interference effectmay cause any fluorophore placed in the right region to fluoresce with aseveral fold higher intensity in comparison to the other regions. Inaddition, the nanospurs 58 positioned along the tips 34 may enhance oramplify the electromagnetic field to create regions along the gratingstructure 10 with an increased electromagnetic field known as hotspots.

In various embodiments, the grating structure 10 may further include asecond functional layer 60, as seen in FIGS. 5 and 6, positioned on theupper surface of the first functional layer 26. Generally, with suchembodiments, the first functional layer 26 is a photonic materialfunctional layer 26 wherein the photonic material is a dielectric suchas titanium oxide. The first functional layer 26 is deposited at angleof approximately zero degrees from planar normal, so that the firstfunctional layer 26 may have a shape as seen in FIG. 1. The secondfunctional layer 60 typically includes plasmonic material such as silverthat is deposited at an angle ranging from greater than zero degrees toapproximately 85 degrees from planar normal. Alternatively, both thefirst functional layer 26 and the second functional layer 60 may includeplasmonic materials.

At least a portion of the steps of a method 100, in accordance withvarious aspects of the invention, for producing a grating structure 10is shown in FIG. 7. The steps of the method 100 may be performed in theorder as shown in FIG. 7, or they may be performed in a different order.Furthermore, some steps may be performed concurrently as opposed tosequentially. In addition, some steps may not be performed.

Referring to step 101, a stamp 38 is formed by applying a flexibleplastic material to a mold 40, shown in FIG. 8, which includes a gratingpattern 42 such that the plastic material receives and retains anegative of the grating pattern 42. The plastic material may include anyflexible, somewhat resilient polymer that can adapt to the shape of amold and retain that shape. An exemplary plastic material ispolydimethylsiloxane (PDMS).

The mold 40 may be any solid object that includes the grating pattern 42on one of its surfaces and may be constructed from materials such asmetals, glass, silicon, or the like. The mold 40 may be produced by anexemplary process described below or by forming the grating pattern 42in the mold 40 material using patterning and etching, e-beamlithography, reactive ion etching, machining, or the like. An exemplarymold 40 is an optical disc, such as a compact disc (CD), a digital videodisc (DVD), a high definition DVD (HD-DVD), a Blu-ray™ disc, etc., whichincludes an internal data layer defined by a grating pattern, the sameas or similar to the grating pattern 42, with a portion of the discremoved to expose the data layer and the grating pattern, as seen inFIG. 8.

The grating pattern 42 may be similar to the array 14, discussed above,wherein the grating pattern 42 includes a plurality of grating elements16 with the characteristics mentioned above. The grating elements 16 ofan exemplary grating pattern 42 may include a longitudinal peak 20positioned next to a longitudinal valley 22 that in combination have across-sectional width of approximately 400 nm.

The plastic material that forms the stamp 38 may initially be in aliquid form and may be applied to the surface of the mold 40 thatincludes the grating pattern 42 by spin coating the plastic materialonto the mold 40 in a known fashion, the result of which is shown inFIGS. 9 and 10. The plastic material may cure on the mold 40 until ithardens and is solid to the touch—thereby forming the stamp 38.

Referring to step 102, the stamp 38, or a portion thereof, is removedfrom the mold 40 and is placed on a temporary substrate 44. Thetemporary substrate 44 is generally a rigid body with at least onesurface that is flat and smooth. An exemplary temporary substrate 44 isa glass slide, a silicon wafer, or the like. After the stamp 38 isformed, as seen in FIGS. 9-11, it may include a first surface 46 whichincludes the negative of the grating pattern 42 and an opposing secondsurface 48 which is generally flat and smooth. The stamp 38 is placed onthe temporary substrate 44 such that the second surface 48 contacts thetemporary substrate 44 and the first surface 46 is exposed andaccessible, as seen in FIG. 12.

Referring to step 103, an ink 50 is formed by applying a polymer film tothe stamp 38 to receive and retain a positive of the grating pattern 42.The polymer film may include any flexible, somewhat resilient polymerthat can adapt to the shape of a mold and retain that shape. Anexemplary polymer film is polymethylsilsesquioxane (PMSSQ). In variousembodiments, the PMSSQ may be mixed with ethanol. The polymer film thatforms the ink 50 may initially be in a liquid form and may be applied tothe stamp 38 by spin coating onto the exposed first surface 46, theresult of which is shown in FIGS. 13 and 14. The polymer film may cureon the stamp 38 until it hardens and is solid to the touch—therebyforming the ink 50. After its formation, the ink 50 may include a firstsurface 52 and an opposing second surface 54, as best seen in FIG. 14.The first surface 52 includes the positive of the grating pattern 42 andis in contact with the first surface 46 of the stamp 38. The secondsurface 54 is generally flat and smooth.

Referring to step 104, nanogaps 30 are created in the ink 50, similar tothose of the base layer 24 seen in FIG. 2. The nanogaps 30 may includetears, openings, or gaps in the polymer material of the ink 50.Exemplary nanogaps 30 may have a width ranging from approximately 20 nmto approximately 30 nm, while the length of the nanogaps 30 may varymore greatly. The nanogaps 30 may be formed by applying a tensionalforce to opposing ends of the stamp 38 and the ink 50 while they are incontact with one another. The nanogaps 30 may also be formed by pokingholes in the combination of the stamp 38 and the ink 50, by bending thecombination of the stamp 38 and the ink 50, or by reverse bending thecombination of the stamp 38 and the ink 50. This step may be optional,it may be performed after the stamp 38 and ink 50 are removed from thetemporary substrate 44, or it may be performed during or after step 105.

Referring to step 105, the stamp 38 and the ink 50 are removed from thetemporary substrate 44 and placed on a permanent substrate 56, as shownin FIGS. 15 and 16. The permanent substrate 56 may be similar to thetemporary substrate 44. An exemplary permanent substrate 56 is a glassslide, a silicon wafer, or the like. The stamp 38 and ink 50 may beremoved from the temporary substrate 44 as a unit while still contactingone another. They may be removed manually by a technician or by anautomated machine. The stamp 38 and ink 50 may be placed on thepermanent substrate 56 with the second surface of the ink 50 contactinga surface of the permanent substrate 56 and the second surface of thestamp 38 facing away from the permanent substrate 56. The placement maybe performed manually or by automated machine. After the placement ofthe stamp 38 and ink 50, a period of time may elapse to allow the ink 50to seal with the permanent substrate 56.

Referring to step 106, the stamp 38 is removed from the ink 50. In someembodiments, the stamp 38 may be peeled from the ink 50 by manuallylifting one corner or edge of the stamp 38, as seen in FIG. 17, with apair of tweezers. In other embodiments, the stamp 38 may be removed fromthe ink 50 by an automated machine. The process of removing the stamp 38from the ink 50 may create nanogaps 30 in the stamp 38 which aretransferred to the ink 50. Thus, after removing the stamp 38 from theink 50, the ink 50 may a plurality of nanogaps 30 that are randomlyoriented and generally positioned in proximity to the perimeter of theink 50. Furthermore, after removing the stamp 38, the first surface 52of the ink 50 is exposed such that the positive of the grating pattern42 is facing upwards. In addition, the ink 50 on the permanent substrate56 generally forms the base layer 24 on the substrate 12 of the gratingstructure 10.

Referring to step 107, a first functional layer 26 is applied to the ink50. The first functional layer 26 is applied to the first surface 52 ontop of the grating pattern 42. The first functional layer 26 may includeplasmonic material, such as metals, or photonic material, such asdielectrics, as discussed above. The first functional layer 26 may beapplied to the ink 50 using known deposition techniques. The firstfunctional layer 26 may also be applied to the ink 50 by chemicalprocedures such as the sol-gel process in which the material of thefirst functional layer 26 is applied to the ink 50 in a solution. Insome embodiments, the material of the first functional layer 26 maydeposited at an angle that is normal to the plane of the ink 50. Theresult of the deposition may be similar to the grating structure 10 asshown in FIGS. 1 and 3. The first functional layer 26 may also beapplied such that it does not fill in or completely cover the nanogaps30 which are formed in the ink 50.

In other embodiments, the material of the first functional layer 26 maydeposited at an angle that is not normal to the plane of the ink 50,similar to the deposition illustrated in FIG. 3. This angled depositionis typically accomplished by tilting the permanent substrate 56 and theink 50 thereupon with respect to the source from which the firstfunctional layer 26 material is deposited. The deposition angle, i.e.,the angle of tilt, may range from approximately zero degrees toapproximately 85 degrees from planar normal. Furthermore, the axis oftilt for the permanent substrate 56 is generally parallel to thelongitudinal axis of the grating elements 16 of the grating pattern 42of the ink 50. The tilting of the permanent substrate 56 and the ink 50during deposition of the first functional layer 26 may result in eachgrating element 16 having the features of the nanogap 32, the tip 34,the plateau 36, and the nanospurs 58, as described above and shown inFIGS. 3 and 4.

The permanent substrate 56 and the ink 50 may have an inherent surfaceenergy or their surface energies may be controlled and adjusted. Thematerial of the first functional layer 26 may have an inherent energylevel or may be given an energy level as well. In addition, the materialof the first functional layer 26 may be ionic in nature. Energies of thematerial of the first functional layer 26, the permanent substrate 56,and the ink 50 may be controlled or adjusted thermally, throughtemperature control, electrically, through voltage control, or by othermethods. The energy levels of one or more of the three components maydetermine the optimal angle for applying the material of the firstfunctional layer 26 in order to form the features of the nanogap 32, thetip 34, the plateau 36, and the nanospurs 58. The physicalcharacteristics of the grating pattern 42 of the ink 50, such as thespacing between grating elements 16, the height of the peak 20, and/orthe aspect ratio of the height to the spacing may also influence thevalue of the optimal angle for applying the material of the firstfunctional layer 26. Furthermore, the thickness of the functional layer26 may influence the value of the optimal angle for applying thematerial of the first functional layer 26. As an example, for an ink 50made from PMSSQ with a grating pattern 42 that is formed from an HD-DVDmold 40 (and has the corresponding spacings and heights) and a firstfunctional layer 26 of silver applied with a thickness of 40 nm, theoptimal angle of deposition is approximately 75 degrees.

In certain embodiments, the first functional layer 26 may include one ormore sublayers of material. For example, when forming a plasmonic firstfunctional layer 26, there may be a sublayer of metal, which enhancesadhesion between the ink 50 and the first functional layer 26. Thesublayers may be deposited onto the ink 50 in the same fashion as thefirst functional layer 26.

Referring to step 108, a second functional layer 60 is applied to thefirst functional layer 26, as shown in FIGS. 5 and 6. This step may beoptional. However, when it is performed, the first functional layer 26typically includes photonic material such as titanium oxide, and thesecond functional layer 60 includes plasmonic material such as silver.Furthermore, the first functional layer 26 is deposited at angle ofapproximately zero degrees from planar normal. The second functionallayer 60 is typically deposited at an angle ranging from greater thanzero degrees to approximately 85 degrees from planar normal.

At least a portion of the steps of a method 200, in accordance withvarious aspects of the invention, for producing a mold 40 with a gratingpattern 42 is shown in FIG. 18. The steps of the method 200 may beperformed in the order as shown in FIG. 18, or they may be performed ina different order. Furthermore, some steps may be performed concurrentlyas opposed to sequentially. In addition, some steps may not beperformed.

Referring to step 201, an optical disc 300 is obtained, including alabel side 302, a transparent side 304, and a metal layer 306, as seenin FIGS. 19 and 21. The optical disc 300 may include a perimeter ring308 and a center ring 310 as well. The optical disc 300 may be of knownoptical data storage disc types with data tracks arranged in concentriccircles. Exemplary optical discs 300 include 12-centimeter diameterdiscs, such as compact disc (CD), digital video disc (DVD), highdefinition DVD (HD-DVD), Blu-ray™ disc, and the like. Typically, theoptical disc 300 is blank (with no pre-recorded data on it), singlesided, and with a single data layer. The label side 302 may be what isconsidered the top surface of the disc, often with a manufacturer's nameor logo on it. The label side 302 may also have an opaque coating. Thetransparent side 304 may be considered the bottom surface of the disc,on the opposite side from the label. The label side 302 and thetransparent side 304 may both include a rigid polymer material, such aspolycarbonate, that gives the optical disc 300 its structure. Duringusage of the optical disc 300, a laser shines light through thetransparent side 304 in order to read data from the optical disc 300.Thus, the transparent side 304 is transmissive to light of varyingwavelengths. The metal layer 306 generally provides reflection of thelaser light which determines the data stored on the optical disc 300.The perimeter ring 308 is a space at the edge of the optical disc 300 inwhich there are no data tracks.

At the metal layer 306, there may be two grating patterns forming thedata tracks, one on the label side 302 and one on the transparent side304, wherein one grating pattern is a mirror image or negative of theother and the metal layer is positioned between the two patterns.Furthermore, the grating patterns may be similar to the grating pattern42 and the array 14 of grating elements 16.

Referring to step 202, a position of the metal layer 306 is determinedwith respect to the label side 302 and the transparent side 304. Thethickness of the optical disc 300 is generally constant for thedifferent types of discs, however the position of the metal layer 306varies with the type. The metal layer 306 in a CD is close to the labelside 302. The metal layer 306 in a DVD and an HD-DVD is positioned nearthe center of the optical disc 300. In a Blu-ray™ disc, the metal layer306 is close to the transparent side 304.

Referring to step 203, the optical disc 300 is split at the metal layer306 along the plane of the disc from the outer edge at the perimeterring 308 toward the center ring 310, if the metal layer 306 is closer tothe transparent side 304 than the label side 302, as seen in FIG. 19.The optical disc 300 is likely a Blu-ray™ disc. An exemplary method tosplitting the optical disc 300 includes cutting the optical disc 300with a sharp object, such as a razor blade, at the edge of the discparallel to its plane. The optical disc 300 usually separates into twopieces along the metal layer 306—the two pieces being the label side 302and the transparent side 304.

Referring to step 204, the transparent side 304 and the metal layer 306are removed from the optical disc 300. Thus, the label side 302 with agrating pattern remain, as seen in FIG. 20. In some cases, fragments ofthe metal layer 306 may remain as well.

Referring to step 205, the optical disc 300 is placed in a solvent toremove any remaining metal. An exemplary solvent includes 15% nitricacid. Other solvents, cleaners, and debris removal techniques may beutilized as well.

Referring to step 206, the perimeter ring 308 is removed from theoptical disc 300, if the metal layer 306 is not closer to thetransparent side 304 than the label side 302, as seen in FIG. 21. Theoptical disc 300 may be a DVD or an HD-DVD. The perimeter ring 308 maybe removed by cutting it off of the optical disc 300 using a sharpobject or by grinding it off. Removal of the perimeter ring 308 may makeit easier to access the metal layer 306 for performing the next step.

Referring to step 207, the optical disc 300 is split at the metal layer306 along the plane of the disc from the outer edge toward the centerring 310. As discussed in step 203, the optical disc 300 separates intotwo pieces, the label side 302 and the transparent side 304, along themetal layer 306.

Referring to step 208, the label side 302 and the metal layer 306 areremoved from the optical disc 300. Thus, the transparent side 304 with agrating pattern remain, as seen in FIG. 22. In some cases, fragments ofthe metal layer 306 may remain as well.

Referring to step 209, the optical disc 300 is placed in a solvent toremove any remaining metal. As with step 205, the solvent may include15% nitric acid. Other solvents, cleaners, and debris removal techniquesmay be utilized as well.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

Having thus described various embodiments of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A grating structure comprising: a base layerpositioned on the substrate, the base layer including a first surfacewith a plurality of grating elements positioned adjacent one another,each grating element including a longitudinal tip, a longitudinalplateau, and a longitudinal nanogap, and a contiguous first functionallayer conformally covering the base layer producing an enhancedfluorescence of a sample, wherein the first functional layer includes aplurality of nanospurs forming a plurality of peaks abutting one anotheralong the length of the longitudinal tip producing additional localizedelectromagnetic field enhancement.
 2. The grating structure of claim 1,wherein the longitudinal nanogap has a width ranging from approximately10 nm to approximately 30 nm and the longitudinal tip has a widthranging from approximately 10 nm to approximately 30 nm.
 3. The gratingstructure of claim 1, wherein the first functional layer is metallic,and wherein the first functional layer is approximately 100 nm thick. 4.The grating structure of claim 1, wherein the first functional layer ismade of silver.
 5. The grating structure of claim 1, wherein the firstfunctional layer is made of a dielectric, and wherein the firstfunctional layer is between approximately 100 nm and approximately 200nm thick.
 6. The grating structure of claim 1, wherein the firstfunctional layer is made of titanium dioxide.